A popular type of magnetic data recording tape is contained within a belt-driven cartridge, commonly called a "tape cartridge" or "data cartridge." The cartridge encloses the tape, which is wound on two reels or hubs driven by a friction-coupled endless internal belt and capstan system in which the belt contacts the periphery of the wound tape and the capstan engages an external drive mechanism in a magnetic tape drive. In this specification and in the claims, the term "tape cartridge" will refer to a belt-driven magnetic recording tape cartridge of this type.
The highly compact and economical data storage provided by these tape cartridges makes them well suited for use in backup and data recovery operations, as well for storage of large volumes of data that does not need to be accessed in a random manner. Presently, these tape cartridges are operated by driving the tape past a read/write head assembly of a tape drive in a linear or longitudinal fashion at speeds between about 25-150 in/s (0.64-3.66 m/s). The magnetic data on the tape is recorded or read in a linear serpentine path.
The relatively high drive speeds and the high density at which magnetic data is recorded on these tapes require that the tape have a modulus of elasticity that is very stable in the longitudinal direction. As a result, the tape cartridges of the present invention are constructed so as to minimize the longitudinal tension on the tape that might otherwise alter the dimensional characteristics of the tape. Unlike conventional audio cassette tapes, for example, which directly drive one of the tape hubs, the tape cartridges of the present invention use the friction-coupled endless internal belt and capstan system to drive the tape past the read/write head assembly without directly tensioning the tape itself.
The minimum requirements for the physical and magnetic interchange of one tape cartridge of this type are presented in American National Standard X3.55-1982 and subsequent Standards incorporating X3.55-1982. Requirements for a similar but smaller "magnetic tape mini-cartridge" are presented in Proposed American National Standard X3B5/87-218, 3rd Draft, Oct. 12, 1987. Alternate standards for tape cartridges have been developed by Quarter Inch Cartridge Drive Standards, Inc. (QIC), Santa Barbara, Calif., such as QIC Development Standards QIC-136, Rev. C, 3 Dec. 1992; QIC-137, Rev. C, 4 Mar. 1993; and QIC-143, Rev. B, 3 Dec. 1992. Tape cartridges configured so as to meet the minimum physical requirements set forth in these type of standards are said to have a "form factor" as generally defined by the peripheral dimensions and configuration specified by the appropriate standard or draft standard.
For a variety of economic and manufacturing reasons, it would be desirable to provide a tape cartridge for a different type of tape drive that has the same form factor as existing tape cartridges. If there are different recording and dimensional characteristics of the magnetic tape for the different tape drive, however, such a tape cartridge must be distinguishable from existing tape cartridges of the same form factor.
Current techniques for distinguishing between different tape cartridges having the same form factor typically rely either on the read/write head assembly to magnetically detect a non-conforming tape format, or on some type of interaction between a physical feature of tape cartridge and a sensing circuit in the tape drive. European Patent Application 0 389 121, for example, describes a data protection feature for a tape cartridge that enables sensing circuitry within the tape drive to distinguish between two different types of tape cartridges having otherwise identical form factors.